SUMMARYIn determining the milk yield of the sow by weighing the litter before and after suckling, loss of weight due to metabolic processes must be considered.An experiment is described to investigate the loss of weight of piglets caused by metabolic processes between two consecutive weighings, and to investigate the relationship between this loss on the one hand and the body weight and the age of the piglets on the other. Weight changes of 15 litters of average 9·8 piglets were studied during 66 weighing periods of 16 minutes, by putting the pigs in a cage, fixed on a differential balance. Each weighing period consisted of 8 periods of 2 minutes, so that in all, loss of weight was studied during 528 2-minute periods.